> From: Michael Sperber <xxxxxx@informatik.uni-tuebingen.de>

    > Tom> While they live on the stack, the only references to these objects are
    > Tom> rooted in $continuation and $environment and follow their respective
    > Tom> chains.  The general collector can regard references from the stack to
    > Tom> the heap as GC roots -- but there's no reason it can't trace those
    > Tom> incrementally.

    > How do you deal with the fact that $continuation changes very
    > frequently? Here's (in my ind) the obvious way to approach this: The
    > GC is tracing some old value of $continuation.  When it's finished,
    > there's a new one there, with new frames hanging off it.  So the
    > tracer needs to go back to the new value.  Is there a guarantee this
    > process will finish if the steps have bounded size?

Right.  There's a bunch of little cases like that in here where you
have to relate the rates of various things going on in order to
guarantee termination of GC phases.  Frankly, I approach hacking Pika
with a kind of iterative deepening of the design space: I'm personally
convinced I can solve that subproblem but I can't, off the top of my
head, demonstrate the solution.

As a general rule, by the time it becomes necessary to blacken
$continuation or $environment in order to close out a trace phase,
make sure that only shallow work is needed.

-t